1. Field of the Invention
The invention concerns a device consisting of at least one Lundström-FET gas sensor, for detecting a gas or a gas mixture.
2. Description of Related Art
Such a device for detecting hydrogen gas is well known from DE 43 33 875 C2. As a gas sensor, it consists of a transistor called the Lundström Field Effect transistor. The Lundström-FET has a gas-sensitive coating which is capacitatively coupled between an electrical insulating coating and the channel domain of the FET. The Lundström-FET works on the basis of the principle that hydrogen atoms separated or adsorbed from the environment become polarized and bring about a change in the threshold voltage of the FET when they reach the boundary between the gas layer and the insulating layer. The disadvantage here, however, is that in order to reach the insulating layer, the hydrogen atom must be diffused through the gas-sensitive layer. For that reason, the Lundström-FET has a relatively slow response time. Admittedly, the response time can be reduced by heating the Lundström-FET, but this requires a not insignificant use of energy. Moreover, the Lundström-FET has a certain sensitivity to other gases besides hydrogen.
A hydrogen detection device is well known from DE 43 33 875 C2, which is a gas-sensor based on the principle of the Suspended Gate Field Effect Transistors (SGFET), with a gas-sensitive coating that is capacitatively coupled across an air gap to a channel domain placed between a Source- and a Drain domain. The gas-sensitive coating reacts when it comes into contact with hydrogen gas, by changing its output, which induces a voltage on the surface of the coating, which sends the current across the channel domain between the Source- and the Drain domain. The gas-sensitive coating, however, is also sensitive to other gases besides hydrogen. In environments in which such other gases might be found, the detection of hydrogen gas can become very imprecise. This is the case, for example, for detecting leaks in the hydrogen fuel lines for motor vehicles using hydrogen as a source of fuel.
Because hydrogen gas is highly explosive when it comes into contact with atmospheric oxygen, any leak must be detected as quickly as possible, in order to either block the delivery of hydrogen and/or to warn the user of the motor vehicle, before a critical concentration of hydrogen gas in the surrounding air is exceeded. However, false alarms which might occur because of the cross-sensitivity of the gas-sensor to other gases should be avoided in all circumstances, since such false alarms might lead to cutting off the supply of hydrogen fuel, and the stalling of the motor vehicle.
The objective therefore is to make to make a device of the above-cited kind, which will make it possible to detect a gas with greater precision and reliability. The other objective is to create a device of the above-cited kind, which will make it possible to detect in a simple fashion, a gas mixture consisting of at least of two gases.